The goal of this 2-year project is to understand the effects of nocturnal life on the function and evolution of the short and middle-to-long wavelength opsin genes and to know whether the opsin sequences of a mammal can help infer the life style (diurnal or nocturnal) of its ancestor. The specific issues are: 1) To test the hypothesis that there was a loss-and-regain of the S and M/L opsins in the ancestral eutherians. 2) To know how fast loss of the S opsin gene can occur under nocturnal life. 3) Has the M/L opsin gene always persisted in all (nocturnal) mammals? 4) Is the M/L opsin locus polymorphic in any (especially nocturnal) prosimians as in the case for New World monkeys? And is it polymorphic in owl monkeys (the only nocturnal New World monkey? 5)Did the common ancestor of higher primates have an M or L opsin? 6) To examine the assumption of long strong nocturnality in several animals. To examine these issues, the PI proposes the following work: 1) Sequence the M/L and S opsin genes in representative individuals from a series of species: Two marsupials (opossum and red-necked wallaby); One monotreme (platypus); One owl monkey and 8 prosimians; Four bats (two mega, two micro); Three rodents; Three carnivores; Study whether there is M/L polymorphism in: Tarsiers; Lemurs; Owl monkeys.